Security element and method for producing the same

ABSTRACT

The invention relates to a security element for security papers, bank notes, ID cards or the like, having at least one plastic layer on which at least two metal layers of different color are so disposed side by side and on the same side of the plastic layer that the different colors are visually checkable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase of PCT application Ser. No.PCT/EP02/14418, filed Dec. 17, 2002.

FIELD OF THE INVENTION

This invention relates to a security element for security papers, banknotes, ID cards or the like, and to a security paper and document ofvalue having such a security element. Further, the invention relates tomethods for producing the security element and the security paper anddocument of value having such a security element.

DESCRIPTION OF THE BACKGROUND ART

EP 0 330 733 A1 proposes a security thread that is testable bothvisually and by machine. For this purpose a transparent plastic foil iscoated metallically and this coating provided with gaps in the form ofcharacters or patterns. Furthermore, the security thread contains in theareas congruent with the gaps chromophoric and/or luminescent substancesthat cause the characters or patterns to differ in color contrast fromthe opaque metal coating under suitable light conditions. The metallayer used is preferably an aluminum layer. This security thread isembedded in security papers as a so-called “window security thread,”i.e. it is quasi woven into the paper during sheet formation of thesecurity paper so that it is freely accessible on the surface of thepaper at regular intervals and completely embedded in the paper only inthe intermediate areas.

This security thread already meets a very high security standard. Thecontinuous metallic coating permits machine testing of electricconductivity, while the gaps serve as a visual authenticity featurereadily recognizable to the viewer in transmitted light. In addition,the thread has an additional feature not readily recognizable to theviewer, namely the luminescence in the area of the gaps, which islikewise testable by machine. When bank notes having such a securitythread are viewed fleetingly, however, the metallic luster of the windowareas is primarily striking. This luster can be imitated by simplygluing aluminum foil elements. Upon a fleeting check solely in reflectedlight, such forgeries could therefore be taken for authentic bank notes.

SUMMARY OF THE INVENTION

The invention is therefore based on the problem of proposing a securityelement as well as a security paper and document of value that haveelevated forgery-proofness in comparison to the prior art.

According to the invention, the security element has at least two metallayers of different color that are disposed on the same surface of thesecurity element and are preferably directly adjacent at least incertain areas. The optical impression of such a security element can beimitated, if at all, only with very high effort, in particular if thedifferent-colored metal layers are applied in complicated patterns,which are possibly also intertwined. For example, a multicolor metallicpicture motif composed of different-colored metals can be produced. Themetal layers are preferably disposed in this connection on a plasticlayer that is part of the security element.

The metal layers need not be disposed in one plane of the securityelement but can be disposed one above the other at least in certainareas. The visible color effect can then be varied via the layerthickness of the metal layers. If at least the layer thickness of theupper layer is selected so thin that it is translucent, the viewerperceives the mixed color of the two metal layers.

The two metal layers can also be disposed one above the other over alarge surface, whereby gaps where the lower metal layer is visible areincorporated in the upper metal layer in certain areas by additionalmeasures. If the lower metal layer also has interruptions that arepreferably offset from the gaps in the upper layer, and the securityelement is disposed so that it is observable on both sides, twodifferent-colored metal layers can be perceived from each side.

Analogously, three and more metal layers can also be disposed one abovethe other and exposed in certain areas by special measures. The metallayers do not necessarily all have to be disposed on the same surface ofthe security element in this connection. The metal layers do not allneed to have a different inherent color either. The color effect canalso be determined by printing a transparent ink.

The metals may be for example aluminum, chrome, nickel, copper, gold,silver or other nonferrous metals or colored metal alloys.Metallic-looking compounds, such as gold-colored titanium nitride, canalso be used.

A further possibility for increasing forgery-proofness is to use metalswith different physical properties, in particular different magnetic orelectric properties. For example, iron and aluminum differ both in theircolor and in their magnetic properties. This difference can be detectedby measurement technology and therefore serves as a machine-detectableauthenticity feature.

Forgery-proofness can be increased additionally if the metal layers havegaps in the form of alphanumeric characters, patterns, logos or thelike.

The security element can be a security thread that consists of aself-supporting plastic foil to which the different-colored metal layersare applied. This security thread can be incorporated at least partly ina security paper or security document. However, it is also possible toform the security element in the form of a band or label and fasten itto the surface of the security paper or document of value.

The plastic foil of the security element can moreover be provided withdiffraction structures in the form of a relief structure. Thediffraction structures can be any diffractive structures such asholograms or grid structures (e.g. kinegrams®, pixelgrams) or the like.

Alternatively, the security element can also be executed as a transferelement. This variant is especially advantageous if the security elementis disposed completely on the surface of the security paper or documentof value. In this case the layer structure of the security element isprepared on a carrier foil, usually a plastic foil, and then transferredto the security paper or document of value in the desired contours by ahot embossing method.

With this security element too, a diffraction structure can of course beintegrated into the layer structure of the security element. Inaddition, the security element can have further security features, suchas a thin-film structure, printed image or the like.

If the security element is disposed on the surface of the security paperor document of value, it can have any outline structures, for exampleround, oval, star-shaped, rectangular, trapezoidal or strip-shapedcontours.

According to a preferred embodiment, the security paper or document ofvalue to which the security element is applied has a through opening.The security element is disposed in this connection in the area of theopening and protrudes beyond it on all sides. In this case the securityelement is checkable from the front and back. The different metals arelikewise recognizable from both sides, absolutely “congruently.”Imitation of the color effect is therefore especially difficult or fullyruled out in this embodiment.

The use of the inventive security element is not limited to the field ofsecurity documents, however. The inventive security element can also beused advantageously in the field of product protection for protectingany goods from forgery. For this purpose, the security element can haveadditional antitheft elements, for example a coil or chip. This appliesanalogously to the security paper or document of value provided withsuch a security element.

The metal layers are preferably applied with a vapor deposition unit,the individual metallic areas each being produced by masks. If more thantwo metal layers are used, individual metal layers can be produced byprinting metallic inks or metal-pigmented inks.

The gaps are preferably produced in the particular metal layers by awashing method as described in WO 99/13157, which is incorporated hereinby reference. The security elements are prepared in this connection as asecurity foil having a plurality of copies of the security element. Thebasic material forms a self-supporting, preferably transparent plasticfoil. This plastic foil corresponds in the case of security threads orlabels to the inventive plastic layer of the security element. When thesecurity elements are detached from an embossed foil, the plastic foilforms the carrier material of this transfer material to which theplastic layer is applied for example in the form of a lacquer layer.Diffraction structures can be embossed into this lacquer layer or, inthe case of security threads or labels, into the plastic foil. Theinventive plastic layer of the security element is printed in the formof the later gaps preferably by intaglio printing. For this purpose anink with a high pigment content is used that forms a pored, raisedinking. The different-colored metal layers are then vapor-deposited onthe printed plastic layer, optionally using masks. In a last step, theinking and the metal layer thereabove are finally removed by washing outwith a fluid, possibly combined with mechanical action. A water-solubleink is preferably used so that water can be used as the fluid. Thismethod thus is non-polluting and does not require any specialprecautions. This method further has the advantage that the gaps areproduced for both or a plurality of metal layers in one operation.Washing out can be supported by mechanical means such as a rotatingcylinder, brush or ultrasound.

The use of etching techniques is much more elaborate but in principlelikewise possible. Here the metal layers are first deposited on theplastic layer and the total surface then printed with a protectivelacquer layer except for the areas to be removed. The total securityelement layer structure is then passed through an etching bath where theuncovered areas are detached from the plastic layer. If differentetching baths are necessary for the different metals, the process ofcovering and immersing in an etching bath must be repeated withdifferent etching solutions. Neutralization and cleaning baths are to beprovided between the individual etching baths so that the chemicals ofthe individual baths are not contaminated.

A further possibility is to produce the gaps in the metal layersgalvanically by electrolysis. Here the metal layers are-likewise firstdeposited on the plastic layer and a passivation layer then printed inthe remaining metallic areas. The security element layer structure isfinally passed through an electrolytic bath using the metal layer as acathode. The electrolytic solution and voltage to be used is to becoordinated with the metals used. Here, too, it might be necessary touse different electrolytic solutions for the different metals. Theprinciple of this method is known to the expert and explained in moredetail e.g. in WO 00/02733, which is likewise incorporated herein byreference.

Other methods are likewise possible, such as removing the metal layerareas mechanically, or producing the interruptions by means of laserscriber, electron-beam erosion or other removal methods.

Luminescent substances, liquid-crystalline substances, metallic printinginks or metal bronzes can be disposed in the metal-layer-freeintermediate areas and serve as a further authenticity feature.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments and advantages of the inventive security element,security paper and document of value will be explained with reference tothe figures. The representations are schematized and do not correspondto the actual ratios of size and proportions.

FIG. 1 shows an inventive document of value,

FIG. 2 shows a cross section through the inventive document of valuealong line A-A,

FIG. 3 shows an inventive security element in a top view,

FIG. 4 shows the layer structure of an embodiment of the securityelement shown in FIG. 3 in cross section,

FIG. 5 shows an inventive transfer material in cross section,

FIG. 6 shows a method for producing an inventive security element,

FIG. 7 shows a further variant of the document of value according toFIG. 1 in cross section along A-A,

FIG. 8 shows an inventive embodiment of a security element in crosssection,

FIG. 9 shows a further inventive embodiment of a security element incross section,

FIG. 10 shows a further inventive embodiment of a security element in atop view,

FIG. 11 shows a method for producing the security element according toFIG. 10,

FIG. 12 shows a method for producing an inventive security element,

FIG. 13 shows a security element produced by the method according toFIG. 12 in a top view.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an inventive document of value in a top view. The shownexample involves bank note 1. Said bank note has strip-shaped securityelement 2 extending over the total width of bank note 1. The totalsurface of security element 2 facing the viewer is metallic, areas 3, 4bearing different-colored metals, which are directly adjacent anddisposed alternatingly in the shown example.

The security element shown in FIG. 1 is a diffractive security elementconsisting of an embossed plastic layer and at least one metallicreflective layer.

FIG. 2 shows a cross section along line A-A in FIG. 1. Here one can seeplastic layer 5 in which diffraction structure 6 is incorporated.Different-colored metal layers 3, 4 are disposed alternatingly directlyadjacent therebelow. The layers of the security element are fastened tothe document of value via adhesive layer 30 in the shown example.

FIG. 3 shows a further embodiment of an inventive security element in atop view. Here, additional gaps 7, 8 are disposed in different metallicareas 3, 4. These gaps may show any signs, alphanumeric characters,patterns, logos or the like. Further, only metallic areas 3, 4 aredirectly adjacent. Between metallic areas 4 and 9 there is largenonmetallic space 12. Likewise metallic area 9 can bear a metal having athird inherent color different from the inherent colors of the metals inareas 3, 4.

The security element shown in FIG. 3 can be for example security thread10, as shown in cross section in FIG. 4. Security thread 10 consists ofpreferably transparent carrier foil 11 on which different-colored metallayers 3, 4, 9 are disposed.

The same appearance as in FIG. 3 can also be shown by a transfermaterial used for producing security elements on security papers,documents of value or the like. Transfer material 13 consists of carrierfoil 14 to which plastic layer 15 is applied. Diffraction structures 6are incorporated in the form of a relief structure in plastic layer 15.Different-colored metal layers 3, 4, 9 are disposed thereabove. Finally,transfer material 13 also has optional adhesive layer 16 that isactivated by heat and pressure in the areas to be transferred upontransfer to the corresponding security paper or document of value forfastening corresponding metal layers 3, 4, 9 and plastic layer 15 to thesecurity paper or document of value. In a last step, carrier foil 14 isremoved.

In gaps 7, 8 and space 12 adhesive layer 16 is directly adjacent todiffraction structure 6. If adhesive layer 16 and plastic layer 15 havea very similar refractive index, diffraction structure 6 is no longer tobe recognized in these areas.

If required by the specific application of the security element, removalof the carrier foil can be dispensed with. The carrier foil can in thisconnection be equipped with good adhesive properties by additionalmeasures.

If the security thread shown in FIG. 4 is likewise to have a diffractionstructure, the latter can be incorporated in carrier foil 11 or aseparate plastic layer disposed between carrier foil 11 and metal layers3, 4.

FIG. 6 shows schematically the method for producing an inventivesecurity element whose metal layers are provided with gaps in certainareas. The method will be explained by way of example for securitythreads or labels, but can of course be used analogously for securityelements with other layer sequences. The security elements arepreferably produced as a security foil having a plurality of copies ofthe security element. The starting point in the example shown here isself-supporting plastic foil 17. It is printed in a first step withhighly pigmented ink 18 in the areas where the gaps are later to bepresent so that a large-pored print arises, as shown in FIG. 6 a).Different-colored metal layers 3, 4 are then applied over total printedplastic foil 17 in the desired form. For this purpose a vapor depositionmethod is preferably used by which individual metals 3, 4 arevapor-deposited on plastic foil 17 successively using masks. In the areaof print 18 no contiguous metal layer is formed due to the poroussurface structure of the ink. The intermediate product provided withmetal layers 3, 4 is shown in FIG. 6 b).

Since no solid metal surface forms in the area of print 18, print 18 andmetal layers 3, 4 present in this area can be removed virtually withouteffort by washing out. Water is preferably used for washing out. Itmight be necessary to additionally use brushes that ensure completeremoval of print 18. The final product is shown in FIG. 6 c). Metallayers 3, 4 have gaps 7, 8. The security foil can finally be cut intosecurity elements of the desired form.

The washing method offers the advantage of obtaining sharp and definededge contours, so that this method can also produce very finehigh-resolution characters or patterns in the metal layers.

In the described examples the surface areas of different metals arepreferably disposed side by side. Despite this the metal layers can alsobe disposed one above the other or in partial overlap. It is onlyimportant that side-by-side metal areas of different color or structureare recognizable upon visual viewing. This is important because it canbe helpful during application of the metal layers if the first metallayer can be disposed over the whole area, the second on partial areasof the first, the third over the whole or part of the area on one orboth preceding layers, etc. This reduces register problems andsimplifies the use of marks.

FIG. 7 shows a corresponding embodiment of the document of value shownin FIG. 1 in cross section along line A-A. In this case securitydocument 1 is provided in the area of security element 2 with all-overmetal layer 4 and metal layer 3 provided only in certain areas so thatmetal layer 4 is recognizable in areas 7. Gaps 7 can likewise beproduced by the “washing method” described above with reference to FIG.6. This method is recommendable in particular when different-coloredmetal layers 3, 4 are prepared on a separate carrier and thentransferred to the document of value or document substrate. Any othermethods for producing the gaps can of course likewise be used. Specialmention should also be made in this context of the removal method bymeans of a laser beam. Here, metal layers 3, 4 are first applied to thedocument of value or a carrier all over. Metal layer 3 is then subjectedin the area of gaps 4 to a laser beam that removes metal layer 3 inthese areas without damaging metal layer 4.

FIGS. 8 and 9 show further embodiments of the inventive security elementprovided with three different-colored metal layers. This variant issuitable in particular for application as a security thread, but is notlimited thereto.

In security thread 10 shown in FIG. 8, carrier foil 11 is provided allover with metal layer 9 having a first color. Metal layers 3 and 4,whose inherent color differs from metal layer 9, are applied thereabove.Metal layers 3 and 4 are provided only in certain areas and can havecongruent gaps 19 in which metal layer 9 is visible. Additionally, metallayer 3 can have gaps 7 where metal layer 4 is visible.

FIG. 9 shows an embodiment wherein metal layer 9 is disposed on theopposite surface of carrier foil 11. In the example shown here, metallayer 9 also has gaps 20. In the example shown here, metal layer 9 canalso consist of the same material as one of metal layers 3, 4. If metallayer 9 is also to have a special inherent color at least in certainareas, it can be printed with transparent color lacquer layer 21.

FIG. 10 shows a further embodiment of an inventive security element in atop view. The security element has in this case two different-coloredmetal layers 3, 4 and further printed image 22 that are disposed inregister. Such a security element is preferably produced by theabove-described washing method.

For this purpose a layer structure as shown in FIG. 11 a is prepared oncarrier material 25. In a first step, metal layer 4 is applied tocarrier material 25 all over. In a next method step, printed image 22 isprinted. Washing ink 18 is applied preferably in overlap and in any casein register with color layer 22. Metal layer 3 is finallyvapor-deposited on this layer structure all over in a furthervapor-depositing step. During the washing operation washing ink 18 isremoved, thereby exposing the areas of printed image 22 covered by saidink, and metal layer 4. FIG. 11 b shows this layer structure in crosssection.

To avoid register problems it might also be expedient to dispose printedimage 22 in the fringe area over washing ink 18, as shown in FIG. 12.During the washing operation the washing ink is dissolved and removedpartly mechanically, thereby also removing the ink thereabove. Thismakes it possible to produce interpenetrating surfaces of differentmetallic color which can additionally be disposed in register with othercolored printed images. Alternatively, however, printed image 22 canalso be disposed under the washing ink.

FIG. 13 shows such a security element after the washing operation in atop view. Here, three circular areas are disposed concentrically.Printed image 22 is disposed in the innermost area. Printed image 22 issurrounded by a circular area of metal layer 3 having a first inherentcolor. This is in turn enclosed by a likewise circular area with metallayer 4. The total area surrounding metal layer 4 is in turn formed bymetal layer 3.

Printed image 22 can consist only of a color layer or else be acomplicated multicolor printed image in the examples shown. This printedimage can also be formed using any inks, such as UV-curable inks,metallic inks or inks with luminescent or optically variable pigmentsadded.

Likewise, the contour forms of the metal layers or printed images shownare not limited to the simple geometrical forms shown. Any complicatedmotifs are possible. The different metal layers can also be separated bydemetalized or unmetalized areas.

Likewise, the embodiments shown can be combined with any furthersecurity features, for example diffraction structures orliquid-crystalline layers.

Finally, the layer sequences shown can also be transferred to anyembodiments of the security element used. Thus, the layer sequencesshown with reference to security threads can be transferred analogouslyto transfer materials or label materials and vice-versa.

1. A method for producing a security element for a security documenthaving at least one plastic layer on which at least two metal layers ofdifferent color are disposed side by side, the metal layers having gapsin the form of alphanumeric characters, patterns, or logos characterizedby the following steps: a) providing the plastic layer in the form of aself-supporting plastic foil or a carrier material on which the plasticlayer is disposed; b) printing the plastic layer with alphanumericcharacters, patterns, or logos; c) using a printing ink with a highpigment content; d) drying the printing ink to form a pored, raisedinking; e) applying the metal layers of different color to the printedplastic layer; f) removing the inking and the metal layers thereabove orpenetrating the inking by washing out with a fluid, possibly combinedwith mechanical action; g) drying and optionally cutting the plasticfoil or carrier material to size.
 2. A method according to claim 1,characterized in that the metal layers are applied by vapor-depositingwith the aid of masks.
 3. A method according to claim 1, characterizedin that before step b) a further metal layer and/or printed image isapplied.
 4. A method according to claim 1, characterized in that theplastic foil or carrier material is provided in the form of an endlessband and the method is performed continuously.
 5. A method according toclaim 1, characterized in that the printing ink is water-soluble andwater is used for washing out.
 6. A method according to claim 1,characterized in that the printing of the plastic layer is done byintaglio printing.
 7. A method according to claim 1, characterized inthat the plastic layer is provided in step a) in the form of an endlessplastic foil and cut in step g) into security threads of predeterminedwidth.
 8. A method according to claim 1, characterized in that theplastic layer is disposed in step a) on a specially prepared carriermaterial to form a transfer material that is cut in step g) into stripsof predetermined width.
 9. A method according to claim 1, characterizedin that a dif-fraction structure is embossed into the plastic layerbefore step b).
 10. A method for producing a security paper forproducing documents of value, characterized in that during theproduction of the security paper a security thread produced according toclaim 1 is embedded.
 11. A method for producing a security paper fordocuments of value, characterized in that a security element producedaccording to claim 1 is applied to the surface of the finished securitypaper.
 12. A method according to claim 11, characterized in that anopening is formed in the security paper during papermaking, which isthen closed with the security element at least on one side.